This invention relates to a method and apparatus for producing metallic rings which are, for example, employed to fabricate starting ring gears for a motor vehicle or the like, and in particular, to a method and apparatus for producing annular metallic blanks for the metallic rings.
There are two conventional methods for producing steel rings which are employed to fabricate ring gears or the like.
In one of the conventional methods for producing steel rings, an elongated steel material such as a steel bar is bent into an annular shape and, then, the ends of such formed steel material are joined together by a welding operation. However, according to this method, when the steel material is bent into an annular shape, the ends of the material are left unformed or straight because the ends are held by gripping means while the material is being bent. Thus, when the ends of the annular material are welded together, the straight ends have to be cut off, and then the ends of the remaining material which has been bent to a predetermined curvature are welded together. The cut off ends are waste. Furthermore, the ends formed by cutting off the straight parts of the annular material are separated from each other, and they have to be butted against each other before they are welded together. The butting operation, however, results in application of an excess amount of stress to the material which may cause deformation of the material into oval or the like shape other than a true circle. In order to check and rectify the deviation from the desired true circular shape, further labor is required and checking and rectifying operations add an additional cost to the production of the rings. Furthermore, since any steel material generally has a variation or deviation in carbon content therein over the length of the material, various portions of the steel material will have somewhat different curvatures, and rectifying operations of such different curvatures also require additional labor and expense.
In the second conventional method, a thick steel cylinder is sliced into a plurality of rings, the diameter of the steel cylinder having a predetermined diameter the same as that of the desired ring products so that the rings formed are, themselves, used as ring products.
In this method, however, a substantial amount of material is wasted as cutting chips when the steel cylinder is sliced, thus resulting in an increase in production cost; Furthermore, the obtained rings are subjected to uneven stress while they are being cut from the steel cylinder and in consequence, the configuration of the obtained rings will come to be distorted, even if the steel cylinder has a relatively precise circular configuration. Such distortion of configuration has to be corrected or rectified and, as with the first conventional method described above, this requires a substantial increase in man hours and expenditure.